WEDNESDAY, Dec. 12, 2018 (HealthDay News) -- For certain men with early prostate cancer, choosing surgery over "watchful waiting" may add a few years to their lives, a new study suggests.

European researchers found that among nearly 700 men with earlier-stage prostate cancer, those who received surgery to remove the gland lived three years longer, on average, than those assigned to watchful waiting.

However, experts had major caveats about the study, which followed men who were treated for prostate cancer 20 to 30 years ago.

Namely, the patients had tumors that were larger and more aggressive than the norm for men diagnosed with early prostate cancer in recent years. So the results cannot be translated to most men diagnosed today, experts said.

"This is an important study with useful information. But it won't change how we manage prostate cancer today," said Dr. Len Lichtenfeld, interim chief medical officer for the American Cancer Society.

The study authors themselves made the same point.

Lead researcher Dr. Anna Bill-Axelson stressed that the patients were different from many men diagnosed with prostate cancer these days -- because they all had "clinically detected" cancer.

Many were diagnosed, for instance, after they developed symptoms of prostate cancer. In other cases, a doctor felt the tumor while doing a rectal exam for other reasons.

In other words, their tumors were advanced enough to cause symptoms or be palpable.

That's in sharp contrast to the situation today, Lichtenfeld said. In the United States, most men are now diagnosed through PSA screening, a blood test that picks up tiny prostate tumors that are not causing any problems.

Often, those men do not need immediate treatment, because prostate cancer is typically slow-growing and may never progress to the point of being life-threatening. Experts say that surgery to remove the gland -- which can cause incontinence and erectile dysfunction -- could do more harm than good.

Instead, men diagnosed through PSA screening can often take a wait-and-see approach -- where their cancer is monitored, and treated only if it progresses.

"The last thing I'd want to see is headlines saying, 'Surgery is better than no surgery,'" Lichtenfeld said. "That's not what this study tells us."

The findings are based on 695 European men diagnosed with prostate cancer that was still confined to the gland.

All were younger than 75 and in good enough health that their life expectancy was at least 10 more years.

Between 1989 and 1999, the men were randomly assigned to either have their prostate gland removed or have their disease monitored.

By 2017, researchers found that 72 percent of surgery patients had died, versus 84 percent of men in the watchful-waiting group. The rate of death from prostate cancer, specifically, was also lower in the surgery group: 20 percent versus 31 percent.

On average, the study found, surgery patients lived three years longer.

But that added life expectancy would not necessarily be seen in men diagnosed through PSA screening, said Bill-Axelson, of Uppsala University in Sweden.

"PSA adds a lead time of at least eight years," she said.

And many of those men, she added, will ultimately develop and die from other health conditions, like heart disease.

That was true even in this study, Bill-Axelson noted, despite the fact that patients were diagnosed with prostate cancer much later than they typically are today.

Overall, she said, about 70 percent of the men died of some other cause.

What about men today whose cancer is not caught by PSA screening, but after they develop symptoms?

Even then, immediate surgery is not always the best option, Lichtenfeld said. There are other factors to weigh, he explained -- such as the size and aggressiveness of the tumor, and a man's age and general health. An elderly man in poor health is unlikely to see any benefit from surgery.

But, Lichtenfeld said, if a man is like those in this study -- with a life expectancy of a decade or more -- surgery is likely to be recommended.

The study appears in the Dec. 13 issue of the New England Journal of Medicine.